Losin' It

Lesson: Good things come to those who wait. And wait. And wait.

Relationships bloomed and fizzled throughout the first seven seasons of Beverly Hills, 90210, but two things remained constant: the steadfast virtue of Donna Martin (Tori Spelling), and the sexual frustration of her on-again, off-again paramour David Silver (Brian Austin Green). But on May 21, 1997, the duo finally consummated their love in a Very Special Episode. Better still, the gal who didn't believe in premarital sex was able to rope her man for good: Some three years later, Donna and David tied the knot on the 90210 series finale.

Lesson: Sex can turn some boys into monsters.

And how, as poor Buffy Summers (Sarah Michelle Gellar) found out after her initial performance of the horizontal mambo with beau Angel (David Boreanaz). As perfect as conditions seemed on the big night — it was Buffy's birthday, she'd just survived (another) near-death experience, and she had to do something to warm up after getting caught in a rainstorm — the morning after went legendarily wrong, with Angel morphing into a soulless bloodsucker hell-bent on destroying the world. Talk about a cautionary tale!

Lesson: It's never as awkward as the first time.

That was the unexpected lesson learned by virgins Seth (Adam Brody) and Summer (Rachel Bilson) during the Valentine's Day episode of The O.C.'s first season. Perhaps in the way some mothers suppress memories of the pain of childbirth, so too can adults forget the clumsiness and misery of their early sexual encounters. But let's allow Seth to remind us: ''It sucked so bad,'' he told Ryan. ''I did make some faces in the middle I wish I could take back.'' Sounds like in this instance, ''the big O'' stood for ''Ouch.''

Lesson: Having sex with your high-school English teacher is illegal. Having sex with said teacher outdoors is just plain stupid.

Not that Pacey (Joshua Jackson) was ever the smartest kid in Capeside, but when his study sessions with Miss Jacobs (Leann Hunley) turned from Ethan Frome to anatomy, you'd think one of 'em would've known enough to keep the affair behind closed doors. Instead, by doing the deed within yards of Dawson's movie shoot, Pacey ensured his, um, maiden voyage was caught on camera — and his ill-advised romance was doomed to fail.

Lesson: Never hang out alone with your married ex-boyfriend. Seriously.

Okay, so maybe Rory (Alexis Bledel) shouldn't have resumed her friendship with still-smitten ex Dean (Jared Padalecki). But who'd have guessed his construction job at the Independence Inn would lead to Rory's sexual awakening, the end of Dean's marriage, and an unwanted eyeful for Lorelai (Lauren Graham)?

Lesson: Some girls mature faster than others.

After nine seasons learning about The Facts of Life, it was bound to happen: One of the sitcom's four disparate young women was about to become — how shall we put this? — not that innocent. Lo and behold, it was full-figured Natalie (Mindy Cohn, far left) who dropped it like it was hot (and then some) on her first anniversary with boyfriend Snake. And no, we're not going to stoop to making obvious jokes about Snake's name: You'll have to insert your own.

Lesson: Not everybody's first time is special.

Exhibit A: University of New York freshman Felicity Porter (Keri Russell). Perpetually torn between dorky resident-adviser Noel and brooding chem major Ben, our heroine's emotional turmoil left her vulnerable when sexy art major Eli (Simon Rex) asked her to swing by the studio to check out his (ahem) sketches. Yet in making her flawed, completely believable decision, Felicity offered gutsy insights on the power of physical attraction, and the fleeting nature of innocence.

Lesson: Beware the power of The Hot Babysitter.

How much you wanna bet Dr. Brown wished he'd hired Nanny McPhee to keep an eye on daughter Delia? Instead, he opted for sexy college student Madison (Sarah Lancaster), an authority figure who ended up deflowering his teenage son, Ephram (Gregory Smith); worse still, the awkward coupling resulted in an unexpected pregnancy for Madison.

Lesson: You can remain a virgin in perpetuity.

Talk about teenage angst! When Angela Chase (Claire Danes) resists temptation and backs out of getting intimate with brooding Jordan Catalano (Jared Leto) at a party in an abandoned house, his response is less than gallant. ''It's accepted. It's what you're supposed to do! Unless you're, like, abnormal,'' he complains. Well, we wouldn't have our heroine any other way. And thanks to the untimely cancellation of ABC's brilliant drama, she'll always be Angela Chaste to us.